Pharmacological treatment for sleep apnea

ABSTRACT

The present invention relates generally to pharmacological methods for the prevention of amelioration of sleep-related breathing disorders via administration of agents or combinations of agents that possess serotonin-related pharmacological activity.

[0001] This international application claims priority to U.S.Provisional Application No. 60/076,216, filed Feb. 27, 1998, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention generally relates to methods for thepharmacological treatment of breathing disorders and, more specifically,to the administration of agents or compositions having serotonin-relatedreceptor activity for the alleviation of sleep apnea (central andobstructive) and other sleep-related breathing disorders.

[0004] 2. Related Technology

[0005] Over the past several years much effort has been devoted to thestudy of a discrete group of breathing disorders that occur primarilyduring sleep with consequences that may persist throughout the wakinghours in the form of sleepiness, thereby manifesting itself intosubstantial economic loss (e.g., thousands of lost man-hours) oremployment safety factors (e.g., employee non-attentiveness duringoperation of heavy-machinery). Sleep-related breathing disorders arecharacterized by repetitive reduction in breathing (hypopnea), periodiccessation of breathing (apnea), or a continuous or sustained reductionin ventilation.

[0006] In general sleep apnea is defined as an intermittent cessation ofairflow at the nose and mouth during sleep. By convention, apneas of atleast 10 seconds in duration have been considered important, but in mostindividuals the apneas are 20-30 seconds in duration and may be as longas 2-3 minutes. While there is some uncertainty as to the minimum numberof apneas that should be considered clinically important, by the timemost individuals come to attention of the medical community they have atleast 10 to 15 events per hour of sleep.

[0007] Sleep apneas have been classified into three types: central,obstructive, and mixed. In central sleep apnea the neural drive to allrespiratory muscles is transiently abolished. In obstructive sleepapneas, airflow ceases despite continuing respiratory drive because ofocclusion of the oropharyngeal airway. Mixed apneas, which consist of acentral apnea followed by an obstructive component, are a variant ofobstructive sleep apnea. The most common type of apnea is obstructivesleep apnea.

[0008] Obstructive sleep apnea syndrome (OSAS) has been identified in asmany as 24% of working adult men and 9% of similar women, with peakprevalence in the sixth decade. Habitual heavy snoring, which is analmost invariant feature of OSAS, has been described in up to 24% ofmiddle aged men, and 14% of similarly aged women, with even greaterprevalence in older subjects.

[0009] Obstructive sleep apnea syndrome's definitive event is theocclusion of the upper airway, frequently at the level of theoropharynx. The resultant apnea generally leads to a progressive-typeasphyxia until the individual is briefly aroused from the sleepingstate, thereby restoring airway patency and thus restoring airflow.

[0010] An important factor that leads to the collapse of the upperairway in OSAS is the generation of a critical subatmospheric pressureduring the act of inspiration that exceeds the ability of the airwaydilator and abductor muscles to maintain airway stability. Sleep plays acrucial role by reducing the activity of the muscles of the upperairways including the dilator and abductor muscles.

[0011] In most individuals with OSAS the patency of the airway is alsocompromised structurally and is therefore predisposed to occlusion. In aminority of individuals the structural compromise is usually due toobvious anatomic abnormalities, i.e, adenotonsillar hypertrophy,retrognathia, or macroglossia. However, in the majority of individualspredisposed to OSAS, the structural abnormality is simply a subtlereduction in airway size, i.e., “pharyngeal crowding.” Obesity alsofrequently contributes to the reduction in size seen in the upperairways. The act of snoring, which is actually a high-frequencyvibration of the palatal and pharyngeal soft tissues that results fromthe decrease in the size of the upper airway lumen, usually aggravatesthe narrowing via the production of edema in the soft tissues.

[0012] The recurrent episodes of nocturnal asphyxia and of arousal fromsleep that characterize OSAS lead to a series of secondary physiologicevents, which in turn give rise to the clinical complications of thesyndrome. The most common manifestations are neuropsychiatric andbehavioral disturbances that are thought to arise from the fragmentationof sleep and loss of slow-wave sleep induced by the recurrent arousalresponses. Nocturnal cerebral hypoxia also may play an important role.The most pervasive manifestation is excessive daytime sleepiness. OSASis now recognized as a leading cause of daytime sleepiness and has beenimplicated as an important risk factor for such problems as motorvehicle accidents. Other related symptoms include intellectualimpairment, memory loss, personality disturbances, and impotence.

[0013] The other major manifestations are cardiorespiratory in natureand are thought to arise from the recurrent episodes of nocturnalasphyxia. Most individuals demonstrate a cyclical slowing of the heartduring the apneas to 30 to 50 beats per minute, followed by tachycardiaof 90 to 120 beats per minute during the ventilatory phase. A smallnumber of individuals develop severe bradycardia with asystoles of 8 to12 seconds in duration or dangerous tachyarrhythmias, includingunsustained ventricular tachycardia. OSAS also aggravates leftventricular failure in patients with underlying heart disease. Thiscomplication is most likely due to the combined effects of increasedleft ventricular afterload during each obstructive event, secondary toincreased negative intrathoracic pressure, recurrent nocturnalhypoxemia, and chronically elevated sympathoadrenal activity.

[0014] Central sleep apnea is less prevalent as a syndrome than OSAS,but can be identified in a wide spectrum of patients with medical,neurological, and/or neuromuscular disorders associated with diurnalalveolar hypoventilation or periodic breathing. The definitive event incentral sleep apnea is transient abolition of central drive to theventilatory muscles. The resulting apnea leads to a primary sequence ofevents similar to those of OSAS. Several underlying mechanisms canresult in cessation of respiratory drive during sleep. First are defectsin the metabolic respiratory control system and respiratoryneuromuscular apparatus. Other central sleep apnea disorders arise fromtransient instabilities in an otherwise intact respiratory controlsystem.

[0015] Many healthy individuals demonstrate a small number of centralapneas during sleep, particularly at sleep onset and in REM sleep. Theseapneas are not associated with any physiological or clinicaldisturbance. In individuals with clinically significant central sleepapnea, the primary sequence of events that characterize the disorderleads to prominent physiological and clinical consequences. In thoseindividuals with central sleep apnea alveolar hypoventilation syndrome,daytime hypercapnia and hypoxemia are usually evident and the clinicalpicture is dominated by a history of recurrent respiratory failure,polycythemia, pulmonary hypertension, and right-sided heart failure.Complaints of sleeping poorly, morning headache, and daytime fatigue andsleepiness are also prominent. In contrast, in individuals whose centralsleep apnea results from an instability in respiratory drive, theclinical picture is dominated by features related to sleep disturbance,including recurrent nocturnal awakenings, morning fatigue, and daytimesleepiness.

[0016] Currently, the most common and most effective treatment, foradults with sleep apnea and other sleep-related breathing disorders aremechanical forms of therapy that deliver positive airway pressure (PAP).Under PAP treatment, an individual wears a tight-fitting plastic maskover the nose when sleeping. The mask is attached to a compressor, whichforces air into the nose creating a positive pressure within thepatient's airways. The principle of the method is that pressurizing theairways provides a mechanical “splinting” action, which prevents airwaycollapse and therefore, obstructive sleep apnea. Although an effectivetherapeutic response is observed in most patients who undergo PAPtreatment, many patients cannot tolerate the apparatus or pressure andrefuse treatment. Moreover, recent covert monitoring studies clearlydemonstrate that long-term compliance with PAP treatment is very poor.

[0017] A variety of upper airway and craniofacial surgical procedureshave been attempted for treatment of OSAS. Adenotonsillectomy appears tobe an effective cure for OSAS in many children, but upper airway surgeryis rarely curative in adult patients with OSAS. Surgical “success” isgenerally taken to be a 50% reduction in apnea incidence and there areno useful screening methods to identify the individuals that wouldbenefit from the surgery versus those who would not derive a benefit.

[0018] Pharmacological treatments of several types have been attemptedin patients with sleep apnea but, thus far, none have proven to begenerally useful. A recent systematic review of these attempts isprovided by Hudgel [J. Lab. Clin. Med., 126:13-18 (1995)]. A number ofcompounds have been tested because of their expected respiratorystimulant properties. These include (1) acetazolamide, a carbonicanhydrase inhibitor that produced variable improvement in individualswith primary central apneas but caused an increase in obstructiveapneas, (2) medroxyprogesterone. a progestin that has demonstrated noconsistent benefit in OSAS, and (3) theophylline, a compound usuallyused for the treatment of asthma, which may benefit patients withcentral apnea but appears to be of no use in adult patients withobstructive apnea.

[0019] Other attempted pharmacological treatment includes theadministration of adenosine, adenosine analogs and adenosine reuptakeinhibitors (U.S. Pat. No. 5,075,290). Specifically, adenosine, which isa ubiquitous compound within the body and which levels are elevated inindividuals with OSAS, has been shown to stimulate respiration and issomewhat effective in reducing apnea in an animal model of sleep apnea.

[0020] Other possible pharmacological treatment options for OSAS includeagents that stimulate the brain activity or are opioid antagonists.Specifically, since increased cerebral spinal fluid opioid activity hasbeen identified in OSAS, it is a logical conclusion that centralstimulants or opioid antagonists would be a helpful treatment of OSAS.In reality, doxapram, which stimulates the central nervous system andcarotid body chemoreceptors, was found to decrease the length of apneasbut did not alter the average arterial oxygen saturation in individualswith obstructive sleep apnea. The opioid antagonist naloxone, which isknown to stimulate ventilation was only slightly helpful in individualswith obstructive sleep apnea.

[0021] Because OSAS is strongly correlated with the occurrence ofhypertension, agents such as angiotensin-converting enzyme (ACE)inhibitors may be of benefit in treating OSAS individuals withhypertension but this does not appear to be a viable treatment for OSASitself.

[0022] Finally, several agents that act on neurotransmitters andneurotransmitter systems involved in respiration have been tested inindividuals with OSAS. Most of these compounds have been developed asanti-depressant medications that work by increasing the activity ofmonoamine neurotransmitters including norepinephrine, dopamine, andserotonin. Protriptyline, a tricyclic anti-depressant, has been testedin several small trials with variable results and frequent andsignificant side effects. As serotonin may promote sleep and stimulaterespiration, tryptophan, a serotonin precursor and selective serotoninreuptake inhibitors have been tested in individuals with OSAS. While apatent has been issued for the use of the serotonin reuptake inhibitor,fluoxetine (U.S. Pat. No. 5,356,934), initial evidence suggests thatthese compounds may yield measurable benefits in only approximately 50 %of individuals with OSAS. Therefore in view of the fact that the onlyviable treatment for individuals suffering from sleep-related breathingdisorders is a mechanical form of therapy (PAP) for which patientcompliance is low, and that hopes for pharmacological treatments haveyet to come to fruition, there remains a need for simplepharmacologically-based treatments that would offer benefits to a broadbase of individuals suffering from a range of sleep-related breathingdisorders. There also remains a need for a viable treatment ofsleep-related breathing disorders that would lend itself to a high rateof patient compliance.

SUMMARY OF THE INVENTION

[0023] The invention is directed to providing pharmacological treatmentsfor the prevention or amelioration of sleep-related breathing disorders.

[0024] The present invention is directed to methods for the preventionor amelioration of sleep-related breathing disorders, the methodcomprising the administration of an effective dose of serotonin receptorantagonist to a patient in need of such therapy. The present inventionis also directed to methods comprising the administration of acombination of serotonin receptor antagonists for the prevention oramelioration of sleep-related breathing disorders. The combination ofserotonin receptor antagonists may be directed to a single serotoninreceptor subtype or to more than one serotonin receptor subtype.

[0025] The present invention is further directed to methods comprisingthe administration of a combination of serotonin receptor antagonists inconjunction with a combination of serotonin receptor agonists for theprevention or amelioration of sleep-related breathing disorders. Thecombination of serotonin receptor antagonists as well as the combinationof receptor agonist may be directed to a single serotonin receptorsubtype or to more than one serotonin receptor subtype.

[0026] The present invention is also directed to methods comprising theadministration of a combination of serotonin receptor antagonists inconjunction with α₂ adrenergic receptor subtype antagonist for theprevention or amelioration of sleep-related breathing disorders. Thecombination of serotonin receptor antagonists may be directed to asingle serotonin receptor subtype or to more than one serotonin receptorsubtype.

[0027] Routes of administration for the foregoing methods may be by anysystemic means including oral, intraperitoneal, subcutaneous,intravenous, intramuscular, transdermal, or by other routes ofadministration. Osmotic mini-pumps and timed-released pellets or otherdepot forms of administration may also be used. The only limitationbeing that the route of administration results in the ultimate deliveryof the pharmacological agent to the appropriate receptor.

[0028] Sleep-related breathing disorders include, but are not limitedto, obstructive sleep apnea syndrome, apnea of prematurity, congenitalcentral hypoventilation syndrome, obesity hypoventilation syndrome,central sleep apnea syndrome, Cheyne-Stokes respiration, and snoring.

[0029] Exemplary serotonin receptor antagonists include, but are notlimited to ondansetron (GR38032F), ketanserin, risperidone,cyproheptadine, clozapine, methysergide, granisetron, mianserin,ritanserin, cinanserin, LY-53,857, metergoline, LY-278,584,methiothepin, p-NPPL, NAN-190, piperazine, SB-206553, SDZ-205,557,3-tropanyl-indole-3 carboxylate, 3-tropanyl-indole-3-carboxylatemethiodide, and other serotonin receptor antagonists.

[0030] Exemplary serotonin receptor agonists include, but are notlimited to 8-OH-DPAT, sumatriptan, L694247(2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl]-1H-indol-3yl]ethanamine),buspirone, alnitidan, zalospirone, ipsapirone, gepirone, zolmitriptan,risatriptan, 311C90, α-Me-5-HT, BW723C86(1-[5(2-thienylmethoxy)-1H-3-indolyl[propan-2-amine hydrochloride), andMCPP (m-chlorophenylpiperazine).

[0031] Exemplary α₂ adrenergic receptor antagonist include, but are notlimited to phenoxybenzamine, phentolamine, tolazoline, terazosine,doxazosin, trimazosin, yohimbine, indoramin, ARC239, and prazosin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 illustrates the effect of serotonin antagonist GR38032F(ondansetron) on the rate of apneas per hour of non-rapid eye movement(NREM) sleep as compared to control. Each data point on the figurerepresents the mean±the standard error for 9 rats (p=0.007 versuscontrol).

[0033]FIG. 2 shows the effect of the serotonin antagonist GR38032F(ondansetron) on the percentage of total recording time spent in NREMsleep as compared to control. Each data point represents the mean ±thestandard error for 9 rats (p=0.0001 versus control).

[0034]FIG. 3 shows the effect of the serotonin antagonist GR38032F(ondansetron) on the rate of apneas per hour of rapid-eye-movement (REM)sleep as compared to control. Each data point represents the mean±thestandard error for 9 rats (p=0.01 versus control).

[0035]FIG. 4 illustrates the effect of the serotonin antagonist GR38032F(ondansetron) on the percentage of total recording time spent in REMsleep as compared to control. Each data point represents the mean±thestandard error for 9 rats.

[0036]FIG. 5 shows the effects of the serotonin antagonist GR38032F(ondansetron) on the rate of normalized minute ventilation duringwakefulness, NREM and REM sleep as compared to control. Each data barrepresents the mean ± the standard error over 6 recording hours with allanimals (n=9) pooled (minute ventilation was significantly largerfollowing GR38032F administration in all behavioral states; p<0.03versus control).

[0037]FIG. 6 shows the effects of serotonin (0.79 mg/kg), GR38032F (0.1mg/kg)+serotonin (0.79 mg/kg), and GR38032F (0.1 mg/kg) on spontaneousapneas in NREM sleep. Each data bar represents the mean±the standarderror over 6 recording hours with all animals (n=10; p=0.97).

[0038]FIG. 7 illustrates the effects of serotonin (0.79 mg/kg), GR38032(0.1 mg/kg) +serotonin (0.79 mg/kg), and GR38032F (0.1 mg/kg) onspontaneous apneas during REM sleep. Each data bar represents themean±the standard error over 6 recording hours with all animals (n=10;p=0.01 for serotonin administration vs. control; p=0.05 foradministration of GR38032F+serotonin vs. serotonin alone; p=0.99 foradministration of GR38032F+serotonin vs. control; and p=0.51 foradministration of GR38032F alone).

DETAILED DESCRIPTION OF THE INVENTION

[0039] Previous studies on the effect of serotonin or serotonin analogson respiration in several anesthetized (see below) animal species havedemonstrated variable responses. For example, administration ofserotonin has been shown to cause an increase in the respiratory ratewith a decrease in tidal volume in rabbits, but an increase in the tidalvolume in dogs [Matsumoto, Arch. Int Pharmacodyn. Ther., 254:282-292(1981); Armstrong et al., J. Physiol. (Lond.), 365:104 P (1985); Bisgardet al., Resp. Physiol. 37:61-80 (1979); Zucker et al. Circ. Res. 47:509-515 (1980). In studies with cats, serotonin administration producedhyperventilation occasionally preceded by apnea [Black et al., Am. J.Physiol., 223:1097-1102 (1972); Jacobs et al., Circ. Res., 29:145-155(1971)], or immediate apnea followed by rapid shallow breathing[Szereda-Przestaszewska et al., Respir. Physiol., 101:231-237 (1995)].

[0040] Administration of 2-methyl-5-hydroxytryptamine, a selective5-hydroxytryptamine₃ receptor agonist, in cat studies caused apnea[Butler et al. Br. J. Pharmacol., 94:397-412 (1988)]. Intravenousadministration of serotonin, 2-methyl-5-hydroxytryptamine or a high doseof α-methyl-5-hydroxytryptamine, a 5-hydroxytryptamine₂ receptoragonist, produced transient apnea, the duration of which increased in adose-dependent fashion. This response was significantly antagonized byGR38032F(1,2,3,9-tetrahydro-9-methyl-3-[(2-methylimidazol-1-yl)methyl]carbazole-4-one,hydrochloride, dihydrate), a selective 5-hydroxytryptamine₃ receptorantagonist [Butler et al. Br. J. Pharmacol., 94:397-412 (1988); Hagan etal., Eur. J. Pharmacol., 138:303-305 (1987)] as well as by ketanserineand methysergide, 5-hydroxytryptamine₂ receptor antagonists [Yoshioka etal., J. Pharmacol. Exp. Ther., 260:917-924 (1992)]. In newborn rats,administration of serotonin precursor L-tryptophan, which activatedcentral serotonin biosynthesis, produced recurrent episodes ofobstructive apnea often followed by central apneas [Hilaire et al., J.Physiol., 466:367-382 (1993); Morin, Neurosci. Lett., 160:61-64 (1993)].

[0041] While the foregoing studies revealed significant informationconcerning the involvement of serotonin in the development of apneas, asstated above one significant problem with all of these studies is thatthe animals were anesthetized, and thus any results obtained could notbe attributed to a specific serotonin agonist or antagonist, i.e., aninteraction with the anesthesia or abnormal physiologic conditionsassociated with the anesthetic could not be ruled out.

[0042] Activity at serotonin receptors may also promote spontaneoussleep-related central apneas, which have been reported in rats,[Mendelson et al., Physiol. Behav., 43:229-234 (1988); Sato et al. Am.J. Physiol., 259:R282-R287 (1990); Monti et al., Pharmacol. Biochem.Behav., 125-131 (1995); Monti et al., Pharmacol. Biochem. Behav.,53:341-345 (1996); Thomas et al., J. Appl. Physiol., 78:215-218 (1992);Thomas et al., J. Appl. Physiol., 73:1530-1536 (1995); Carley et al.Sleep, 19:363-366 (1996); Carley et al., Physiol. Behav., 59:827-831(1996); Radulovacki et al., Sleep, 19:767-773 (1996); Christon et al.,J. Appl. Physiol., 80:2102-2107 (1996)]. In order to test thishypothesis, experiments were conducted to test the effects of aserotonin antagonist in freely moving animals in order to assess whetherblockade of serotonin receptors would inhibit expression of spontaneousapneas during NREM sleep and REM sleep. Experiments were also conductedto test the effects of serotonin and serotonin antagonists, singly andin combination, in freely moving animals in order to assess whetherincreased serotonergic activity at peripheral serotonin receptors maypromote sleep apneas.

[0043] The following examples illustrate the effects of administrationof serotonin receptor antagonists, and in particular GR38032F, to causesuppression of central apneas during non rapid eye movement (NREM) andespecially during rapid eye movement (REM) sleep. This effect wasassociated with increased respiratory drive but did not causecardiovascular changes at the dose tested.

[0044] The following examples also illustrate the effects of serotoninadministration to induce spontaneous apnea expression, which wascompletely antagonized via the administration of serotonin receptorantagonists, and in particular GR38032F.

[0045] The following examples further describe the pharmacologicalprofiles best suited for single agents or combinations of agents tosuccessfully prevent or ameliorate sleep-related breathing disorders,i.e.,

[0046] (a) a single agent or combination of agents having either5-hydroxytryptamine₂ or 5-hydroxytryptamine₃ receptor subtypeantagonistic activity or both;

[0047] (b) a single agent or combination of agents having either5-hydroxytryptamine₂ or 5-hydroxytryptamine₃ receptor subtypeantagonistic activity or both in conjunction with either5-hydroxytryptamine₁ or 5-hydroxytryptamine₂ receptor subtype agonisticactivity or both; or

[0048] (c) a single agent or combination of agents having either5-hydroxytryptamine₂ or 5-hydroxytryptamine₃ receptor subtypeantagonistic activity or both in conjunction with α₂ adrenergic receptorsubtype antagonistic activity.

[0049] Further aspects of the invention and embodiments will be apparentto those skilled in the art. In order that the present invention isfully understood, the following examples are provided by way ofexemplification only and not by way of limitation.

[0050] Example 1 describes the preparation of the animals for treatmentwith either serotonin antagonists or agonists or both and subsequentphysiological recording and testing.

[0051] Example 2 describes the methods for the physiological recordingof treatment and control animals and results obtained fromadministration of a serotonin antagonist.

[0052] Example 3 describes results obtained from the administration ofserotonin followed by the administration of a serotonin receptorantagonist.

[0053] Example 4 describes agents or compositions that posses a specificserotonin-related pharmacological activity that is used to effectivelysuppress or prevent sleep-related breathing disorders.

[0054] The following examples are illustrative of aspects of the presentinvention but are not to be construed as limiting.

EXAMPLE 1 Preparation of Animals for Physiological Testing and Recording

[0055] Adult, male Sprague-Dawley rats (Sasco-King, Wilmington, Mass.;usually 8 per test group; 300 g) were maintained on a 12-hour light(08:00-20:00 hour)/12-hour dark (20:00-08:00 hour) cycle for one week,housed in individual cages and given ad libirum access to food andwater. Following the one week of acclimatization, animals were subjectedto the following surgical procedures.

[0056] Acclimatized animals were anesthetized for the implantation ofcortical electrodes for electroencephalogram (EEG) recording and neckmuscle electrodes for electromyogram (EMG) recording using a mixture ofketamine (Vedco, Inc., St. Joseph, Mo.; 100 mg/ml) and acetylpromazine(Vedco, Inc., St. Joseph, Mo.; 10 mg/ml; 4:1, volume/volume) at a volumeof 1 ml/kg body weight. The surface of the skull was exposed surgicallyand cleaned with a 20% solution of hydrogen peroxide followed by asolution of 95% isopropyl alcohol. Next, a dental preparation of sodiumfluoride (Flura-GEL®, Saslow Dental, Mt. Prospect, Ill.) was applied toharden the skull above the parietal cortex and allowed to remain inplace for 5 minutes. The fluoride mixture was then removed from theskull above the parietal cortex. The EEG electrodes consisting of fourstainless steel machine screws, having leads attached thereto, werethreaded into the skull to rest on the dura over the parietal cortex. Athin layer of Justi® resin cement (Saslow Dental, Mt. Prospect, Ill.)was applied to cover the screw heads (of screws implanted in the skull)and surrounding skull to further promote the adhesion of the implant.EMG electrodes consisting of two ball-shaped wires were inserted intothe bilateral neck musculature. All leads (i.e., EEG and EMG leads) weresoldered to a miniature connector (39F1401, Newark Electronics,Schaumburg, Ill.). Lastly, the entire assembly was fixed to the skullwith dental cement.

[0057] After surgery, all animals were allowed to recover for one weekbefore being subjected to another surgery that involved implantation ofa radiotelemetry transmitter (TA11-PXT, Data Sciences International, St.Paul, Minn.) for monitoring blood pressure (BP) and heart period (HP),estimated as pulse interval. After the animals were anesthetized (asdescribed above), the hair from the subxiphoid space to the pelvis wasremoved. The entire area was scrubbed with iodine and rinsed withalcohol and saline. A 4-6 cm midline abdominal incision was made toallow good visualization of the area from the bifurcation of the aortato the renal arteries. A retractor was used to expose the contents ofthe abdomen and the intestine was held back using saline moistened gauzesponges. The aorta was dissected from the surrounding fat and connectivetissues using sterile cotton applicators. A 3-0 silk suture was placedbeneath the aorta and traction was applied to the suture to restrict theblood flow. Then the implant (TA11-PXT) was held by forceps while theaorta was punctured just cranial to the bifurcation using a 21-gaugeneedle bent at the beveled end. The tip of the catheter was insertedunder the needle using the needle as a guide until the thin-walled BPsensor section was within the vessel. Finally, one drop of tissueadhesive (Vetbond®, 3M, Minneapolis, Minn.) was applied to the puncturesite and covered with a small square of cellulose fiber (approximately 5mm² ) so as to seal the puncture after catheter insertion. The radioimplant was attached to the abdominal wall by 3-0 silk suture, and theincision was closed in layers. After the second surgery, animals wereagain allowed a one week recovery period prior to administration of theserotonin receptor antagonist and subsequent physiological recording.

EXAMPLE 2 Physiological Recording and Suppression of Apneas

[0058] Physiological parameters (see below) from each animal wererecorded on 2 occasions in random order, with recordings for anindividual animal separated for at least 3 days. Fifteen minutes priorto each recording each animal received a systemic injection (1 ml/kgintraperitoneal bolus injection) of either saline (control) or 1 mg/kgof ondansetron (GR38032F;1,2,3,9-tetrahydro-9-methyl-3-[(2-methylimidazol-1-yl)methyl]carbazole-4-one,hydrochloride, dihydrate; Glaxo Wellcome, Inc., Research Triangle Park,N.C.). Polygraphic recordings were made from hours 10:00-16:00.

[0059] Respiration was recorded by placing each animal, unrestrained,inside a single chamber plethysmograph (PLYUN1R/U; Buxco Electronics,Sharon, Conn.; dimension 6 in.×10 in.×6 in.) ventilated with a bias flowof fresh room air at a rate of 2 L/min. A cable plugged onto theanimal's connector and passed through a sealed port was used to carrythe bioelectrical activity from the head implant. Respiration, bloodpressure, EEG activity, and EMG activity were displayed on a videomonitor and simultaneously digitized 100 times per second and stored oncomputer disk (Experimenter's Workbench; Datawave Technologies,Longmont, Colo.).

[0060] Sleep and waking states were assessed using the biparietal EEGand nuchal EMG signals on 10-second epochs as described by Bennington etal. [Sleep, 17:28-36 (1994)]. This software discriminated wakefulness(W) as a high frequency low amplitude EEG with a concomitant high EMGtone, NREM sleep by increased spindle and theta activity together withdecreased EMG tone, and REM sleep by a low ratio of a delta to thetaactivity and an absence of EMG tone. Sleep efficiency was measured asthe percentage of total recorded epochs staged as NREM or REM sleep.

[0061] An accepted physiological animal model [rat; Monti, et al.,Pharamcol. Biochem. Behav., 51:125-131 (1995)] of spontaneous sleepapnea was used to assess the effects of GR38032F. More specifically,sleep apneas, defined as cessation of respiratory effort for at least2.5 seconds, were scored for each recording session and were associatedwith the stage of sleep in which they occurred: NREM or REM sleep. Theduration requirement of 2.5 seconds represented at least 2 “missed”breaths, which is therefore analogous to a 10 second apnea durationrequirement in humans, which also reflects 2-3 missed breaths. Theevents detected represent central apneas because decreased ventilationassociated with obstructed or occluded airways would generate anincreased plethysmographic signal, rather than a pause. An apnea index(AI), defined as apneas per hour in a stage were separately determinedfor NREM and REM sleep. The effects of sleep stage (NREM vs. REM) andinjection (control vs. GR30832F) were tested using ANOVA with repeatedmeasures. Multiple comparisons were controlled using Fisher's protectedleast significant difference (PLSD). In addition, the timing and volumeof each breath were scored by automatic analysis (Experimenters'Workbench; Datawave Technologies, Longmont, Colo.). For each animal themean respiratory rate (RR) and minute ventilation (MV) was computed forW throughout the 6 hour control recording and used as a baseline tonormalize respiration during sleep and during GR38032F administration inthat animal. One way ANOVA was also performed by non-parametric(Kruskal-Wallis) analysis. Conclusions using parametric andnon-parametric ANOVA were identical in all cases.

[0062] Similar software (Experimenters' Workbench; DatawaveTechnologies, Longmont, Colo.) was employed to analyze the bloodpressure waveform; for each beat of each recording, systolic (SBP) anddiastolic (DBP) blood pressures and pulse interval were measured. Thepulse interval provided a beat by beat estimate of HP. Mean BP (MBP) wasestimated according to the weighted average of SBP and DBP for eachbeat: MBP=DBP+(SBP-DBP)/3. The parameters for each beat were alsoclassified according to the sleep/wake state and recording hour duringwhich they occurred.

[0063] Results of the administration of the serotonin antagonistGR38032F on the rate of apneas per hour of NREM sleep during the 6 hoursof polygraphic recording (see FIG. 1) demonstrated no significant effectof treatment or time over 6 hours (two-way ANOVA). However, there was asignificant suppression of apneas during the first 2 hours of recordingas determined by paired t-tests (p<0.01 for each). This respiratoryeffect was associated with a significant suppression of NREM sleep bythe GR38032F during the first 2 hours as demonstrated in FIG. 2. Thepercentage of NREM sleep in 6 hour recordings was lower in GR38032Fadministered rats than in controls, but the decrease reached statisticalsignificance only during the first 2 hours of the recordings (p<0.001).

[0064] Results further indicated a significant suppressant effect ofGR38032F on REM sleep apneas throughout the 6 hour recording period(p=0.01 for drug effect on 2-way ANOVA; see FIG. 3). This effect wasparticularly manifest during the first 4 hours of recordings, duringwhich no animal exhibited a single spontaneous apnea in REM sleep. Thiseffect was not a simple reflection of REM suppression during the first 4hours.

[0065] Results set forth in FIG. 4 show that GR38032F did notsignificantly affect REM sleep. Although REM sleep in drug treatedanimals was lower than in corresponding controls it did not reachstatistical significance overall or during any single recording hour.

[0066] Results of the administration of GR38032F on the normalizedminute ventilation during W (wake), NREM (non-rapid eye movement) sleep,and REM (rapid eye movement) sleep (see FIG. 5) indicate a significantstimulation of ventilation during all behavioral states (p=0.03 foreach). Finally, results indicate that GR38032F had no effect on anycardiovascular variable (MBP and HP during W, NREM, and REM sleep)measured (p>0.1 for each variable; see Table 1). TABLE 1 Effects ofGR38032F on Cardiovascular Variables Mean BP (mm Hg) HP (msec) W NREMREM W NREM REM Control 111 ± 18 110 ± 18 108 ± 18 174 ± 5 181 ± 5 185 ±6 GR38032F 113 ± 18 112 ± 17 110 ± 17 183 ± 3 189 ± 3 190 ± 3

[0067] Overall these results indicate that the manipulation ofserotonergic systems can exert a potent influence on the generation ofcentral apneas in both REM and NREM sleep. Specifically the presentfindings indicate that systemic administration of a 5-hydroxytryptamine₃receptor antagonist suppresses spontaneous apnea expression; completelyabolishing REM-related apnea for at least 4 hours after intraperitonealinjection. This apnea suppression was associated with a generalizedrespiratory stimulation that was observed as increased minuteventilation during both waking and sleep. These significant respiratoryeffects were observed at a dose which caused no change in heart rate orblood pressure, even during the first 2 hours, when respiration wasmaximal.

[0068] Those of skill in the art will recognize that exemplary serotoninreceptor antagonists include, but are not limited to (a) ketanserin,cinanserin, LY-53,857, metergoline, LY-278,584, methiothepin, p-NPPL,NAN-190, piperazine, SB-206553, SDZ-205,557,³-tropanyl-indole-3-carboxylate, 3-tropanyl-indole-3-carboxylatemethiodide, and methysergide (Research Biochemicals, Inc., Natick,Mass.); (b) risperidone (Janssen Pharmaceutica, Titusville, N.J.); (c)cyproheptadine, clozapine, mianserin, and ritanserin (Sigma ChemicalCo., St. Louis, Mo.); (d) granisetron (SmithKline Beecham, King ofPrussia, Pa.); and other serotonin receptor antagonists may be used toprevent or ameliorate sleep-related breathing disorders. Further, thoseof skill in the art will also recognize that the results discussed abovemay be easily correlated to other mammals, especially primates (e.g.,humans).

EXAMPLE 3 Induction and Suppression of Sleep Apneas

[0069] Administration of serotonin or serotonin analogs producedvariable respiratory responses in anesthetized animals of severalspecies (see above, DETAILED DESCRIPTION OF THE INVENTION). As shownabove in Example 2, intraperitoneal administration of 1 mg/kg GR38032F,a selective 5-hydroxytryptamine₃ receptor antagonist, suppressedspontaneous central apneas. This effect was especially prominent in REMsleep, during which apneas were completely abolished for at least 4hours following injection. The apnea suppressant effect of GR38032F wasparalleled by increased respiratory drive, but BP and heart rate changeswere absent at the dose tested.

[0070] Suppression of spontaneous apneas during natural sleep byGR38032F (see Example 2) is consistent with prior studies inanesthetized rats, wherein 5-hydroxytryptamine and2-methyl-5-hydroxytryptamine, a selective 5-HT₃ receptor agonist,provoked central apneas that were antagonized by GR38032F. Since5-hydroxytryptamine does not penetrate the blood-brain barrier (BBB),these results (from the prior studies) indicate that stimulation ofperipheral 5-hydroxytryptamine receptors, and more particularly5-hydroxytryptamine₃ receptors seemed to have provoked the occurrence ofcentral apneas. In view of that study, performed in anesthetizedanimals, as well as our study (described in Example 2 above) in freelymoving rats with respect to administration of GR38032F, we studied theability of increased serotonergic activity at peripheral5-hydroxytryptamine receptors, and more specifically,5-hydroxytryptamine₃ receptors to promote spontaneous sleep-relatedcentral apneas and whether any induction of apneas would be susceptibleto antagonism by administration of 5-hydroxytryptamine receptorantagonists.

[0071] Ten adult male Sprague-Dawley rats (Sasco-King, Wilmington,Mass.; 300 g) were maintained on a 12-h light (08:00-20:00 hour)/12-hourdark (20:00-08:00) cycle for one week, housed in individual cages, andgiven ad libirurn access to food and water. Following the one week ofacclimatization, animals were prepared for physiological testing via thesurgical procedures (i.e., implantation of cortical electrodes for EEGrecording and neck muscle electrodes for EMG recording, implantation ofa radiotelemetry transmitter for BP and HP monitoring) as set forthabove in Example 1. After completion of the surgical procedures, animalswere allowed a one week recovery period prior to use in the presentstudy.

[0072] Each animal was recorded on four occasions, with recordings foran individual animal separated by at least three days. Fifteen minutesprior to each recording, each animal received (via intraperitonealinjection), in random order, one of the following: (a) saline solution(control); (b) 0.79 mg/kg serotonin; (c) 0.1 mg/kg GR38032F plus 0.79mg/kg serotonin; or (d) 0.I mg/kg GR38032F. For the GR38032F+serotonintest group, 0.1 mg/kg GR38032F was administered at time 09:30 followedby 0.79 mg/kg serotonin at time 09:45. Polygraphic recordings were madefrom 10:00-16:00.

[0073] Respiration BP, EEG, and EMG data were determined and recordedvia the experimental procedure as specifically set forth above inExample 2. As in Example 2, sleep apneas, defined as cessation ofrespiratory effort for at least 2.5 s, were scored for each recordingsession and were associated with the stage in which they occurred: NREMor REM sleep. The duration requirement of 2.5 s represents at least two“missed” breaths, which is analogous to a 10-s apnea durationrequirement in humans.

[0074] The effects of sleep stage (NREM vs REM) and injection (controlvs. administration of either serotonin alone, GR38032F+serotonin, orGR38032F alone) on apnea indexes, respiratory pattern, BP, and HP weretested using analysis of variance (ANOVA) with repeated measures.Multiple comparisons were controlled using Fisher's protectedleast-significance difference (PLSD). One-way ANOVA was also performedby nonparametric (Kruskal-Wallis) analysis. Conclusions using parametricand nonparametric ANOVA were identical in all cases.

[0075] Results of the administration of either serotonin alone (0.79mg/kg), GR38032F (0.1 mg/kg)+serotonin (0.79 mg/kg), or GR38032F alone(0.1 mg/kg) on the ability to promote spontaneous apneas in NREM sleepduring a 6 hour polygraphic recording is set forth in FIG. 6.Specifically, during NREM sleep, the spontaneous apnea index was notaffected by any drug treatment.

[0076] As illustrated in FIG. 7, spontaneous apnea expression during REMsleep significantly increased following administration of serotonin ascompared to control recording (>250% increase). Results also indicatethat such an increase was abolished via prior administration ofGR38032F. At the low dose tested (0.1 mg/kg) administration of GR38032Falone had no effect on REM sleep spontaneous apneas.

[0077] As set forth in Table 2 (percentages of waking, NREM, and REMsleep during 6 hours of polygraphic recording following drugadministration), intraperitoneal administration of serotonin alone,GR38032F+serotonin, or GR38032F alone had no effect on sleeparchitecture. Finally, no treatment group tested had a significanteffect on RR, VE, mean BP, HP, or PS apnea index (data not shown). TABLE2 Effects of 5-HT and GR38032F on Sleep/Wake Architecture % Wakefulness% NREM % REM Control (saline solution)  33.7 ± 2.5* 58.0 ± 1.9 6.9 ± 1.15-HT (0.79 mg/kg) 30.2 ± 3.2 59.9 ± 3.3 6.5 ± 1.1 5-HT + GR38032F 36.7 ±8.7 56.0 ± 7.6 5.3 ± 1.4 GR38032F (0.1 mg/kg) 28.8 ± 6.4 63.4 ± 5.7 7.3± 2.3 p (1-way ANOVA) 0.43 0.71 0.60

[0078] Overall these results indicate that manipulation of peripheralserotonin receptors exerts a potent influence on the generation ofcentral apneas during REM sleep. Specifically, the present results showthat systemic administration of serotonin increases spontaneous apneaexpression in sleep. Although the dose of serotonin employed had noeffect on sleep, cardiovascular variables, RR, or VE, the REM-relatedspontaneous apnea index increased >250%. Further, it is important tonote that the mechanisms of apnea genesis are at least partiallysleep-state specific, as NREM apneas were unaffected.

[0079] These findings demonstrate that exogenous administration of5-hydroxytryptamine₃ agonists and antagonists at various doses produceschanges in apnea expression that are specific to REM sleep. Suchfindings indicate that there is a physiologic role for endogenousserotonergic activity in modulating the expression of apnea, especiallyduring REM sleep. Moreover, because serotonin does not cross theblood-brain barrier, the finding that serotonin exerts a converse effectto GR38032F indicates that the relevant receptors are located in theperipheral nervous system. Further, the present data suggest that theaction of supraphysiologic levels of serotonin on apneas is receptormediated in that pretreatment with a low dose (0.1 mg/kg) of GR38032F,which had no independent effect on any measured parameter, includingapneas, fully blocked the effects of exogenous serotonin on apneaexpression.

[0080] In view of the foregoing data, the likely peripheral site ofaction for the observed apnea-promoting effects of serotoninadministration is thought to be the nodose ganglia of the vagus nerve.More specifically, several studies have concluded that the apneacomponent of the Bezold-Jarisch reflex results from the action ofserotonin at the nodose ganglia in cats [Jacobs et al., Circ. Res.,29:145-155 (1971), Sampson et al., Life Sci., 15:2157-2165 (1975),Sutton, Pfllugers Arch., 389:181-187 (1981)] and rats [Yoshioka et al.,J. Pharmacol. Exp. Ther., 260:917-924 (1992) and McQueen et al., J.Physiol., 5073:843-855 (1998)]. Intravenous administration of serotoninor 5-hydroxytryptamine₃ receptor agonists also stimulates pulmonaryvagal receptors [McQueen et al., J. Physiol., 5073:843-855 (1998)],which may contribute significantly to the apneic response.

[0081] Although species differences may be present [Black et al., Am. J.Physiol., 223:1097-1102 (1972)], several studies in rat demonstratethat, in addition to its impact on vagal signaling, serotonin alsoelicits increased firing from carotid body chemoreceptors [McQueen etal., J. Physiol., 5073:843-855 (1998); Sapru et al., Res. Comm. Chem.Pathol. Pharmacol.; 16:245-250 (1977); Yoshioka, J. Pharmacol. Exp.Ther., 250:637-641 (1989) and Yoshioka et al., Res. Comm. Chem. Pathol.Pharmacol., 74:39-45 (1991)] and increased VE [McQueen et al., J.Physiol., 5073:843-855 (1998); Sapru et al., Res. Comm. Chem. Pathol.Pharmacol., 16:245-250 (1977)]. Although chemoreceptor-mediated effectson apnea cannot be ruled out, the data of McQueen et al., J. Physiol.,5073:843-855 (1998) strongly indicate that intravenous serotonin elicitsapnea via a vagal pathway, while the chemoreceptor activation opposesapnea genesis in the anesthetized rat.

[0082] The serotonin-induced Bezold-Jarisch reflex in anesthetizedanimals includes apnea and bradycardia. At the dose employed, serotonindid not elicit changes in either heart rate or mean BP over the 6 hourrecording period. Beat-to-beat heart rate and BP variability, assessedas coefficients of variation, were also unaffected by serotonin at thedose tested. The observed dissociation of cardiovascular and respiratoryresponses to serotonin indicates that changes in apnea expression werenot baroreceptor mediated.

[0083] Although the Bezold-Jarisch reflex in anesthetized animals andserotonin-induced apneas in REM sleep are not the same phenomenon, theymay be related by similar mechanisms. When serotonin receptors arestrongly manipulated by exogenous means, i.e., either with serotonergicagonists or antagonists, the expression of spontaneous apneas in REMsleep can be amplified or suppressed. However, our observation that 1mg/kg GR38032F significantly suppressed REM apneas does not preclude arole for 5-hydroxytryptamine₂ or other 5-hydroxytryptamine receptorsubtypes in the peripheral regulation of the apnea expression, andinfact the invention also contemplates the use of 5-hydroxytryptamine₂and 5-hydroxytryptamine₃, alone or in combination as well as serotoninantagonists that exhibit both type 2 and type 3 receptor antagonism (seeExample 4).

[0084] It has been well established [Mendelson et al., Physiol. Behav.,43:229-234 (1988); Sato et al., Am. J. Physiol., 259:R282-287 (1990);Monti et al., Pharmacol. Biochem. Behav., 51:125-131 (1995); Monti etal., Pharmacol. Biochem. Behav., 53:341-345 (1996); Thomas et al., J.Appl. Physiol., 73:1530-1536 (1992) and Thomas et al., J. Appl.Physiol., 78:215-218 (1995)] that apnea frequency in rats increases fromdeep slow-wave sleep to light NREM sleep to REM sleep, as is the case inman. The high incidence of apnea expression during REM sleep may berelated to respiratory changes that take place during this sleep state.Typically, during REM sleep, breathing becomes shallow and irregular[Orem et al., Respir. Physiol., 30:265-289 (1977); Phillipson, Annu.Rev. Physiol., 40:133-156 (1978); Sieck et al., Exp. Neurol., 67:79-102(1980) and Sullivan, In:Orems et al., eds., “Physiology in sleep,”Academic Press, New York, N.Y., pp. 213-272 (1980)] and VE is at itslowest point [Hudgel et al., J. Appl. Physiol., 56:133-137 (1984)]. Thisbackground of low respiratory output coupled with strong phasic changesin autonomic activity [Mancia et al., In; Orem et al., eds., “Physiologyin sleep,” Academic Press, New York, N.Y., pp. 1-55 (1980)] would renderrespiratory homeostasis during REM sleep more vulnerable to interruptionby apnea. Thus it is possible that the role of serotonin activity in theperipheral nervous system in REM apnea genesis may arise from aserotonergic modulation of either tonic or phasic activity ofrespiratory afferent activity, especially in the vagus nerves.Therefore, the brainstem respiratory integrating areas may be renderedmore vulnerable to fluctuating afferent inputs during REM sleep.

[0085] Overall, the results presented herein indicate that theexacerbation of spontaneous apnea during REM sleep produced byperipherally administered serotonin is receptor mediated. Such findingsalso indicate a physiologic role for endogenous serotonin in theperipheral nervous system in modulating sleep apnea expression underbaseline conditions.

EXAMPLE 4 Suppression or Prevention of Sleep Apneas

[0086] As indicated by the data presented herein (see Examples 2 and 3)serotonin plays an important and integral role in apnea genesis, whichis both highly site and receptor subtype specific. More specifically,the efficacy of a serotonin receptor antagonist to suppress apnea isbased on its activity in the peripheral nervous system, with the nodoseganglia of the vagus nerves appearing to be a crucial target site.5-hydroxytryptamine₂ and 5-hydroxytryptamine₃ receptors at this site areclearly implicated in serotonin-induced apnea in anesthetized animals[Yoshioka et al, J. Pharmacol. Exp. Therp., 260:917-924 (1992)]. Inconjunction with these previous findings, the data presented herein(that administration of serotonin strictly to the peripheral nervoussystem exacerbates sleep-related apnea) indicates the importance ofnodose ganglion serotonin receptors of both types in sleep apneapathogenesis. Moreover, the serotonin-induced increase in apneaexpression was completely blocked by a low dose of GR38032F, a5-hydroxytryptamine₃ antagonist. Such a result indicates that thepreviously demonstrated suppression of apnea by GR38032F (see Example 2)most probably resulted from activity in the peripheral nervous system.

[0087] Therefore, in view of the foregoing, sleep related breathingdisorders (sleep apnea syndrome, apnea of infancy, Cheyne-Stokesrespiration, sleep-related hypoventilation syndromes) may be effectivelyprevented or suppressed via systemic administration of pharmacologicalagents exhibiting either serotonin type 2 or type 3 receptor antagonism,alone or in combination as well as agents that exhibit both serotonintype 2 and type 3 receptor antagonism.

[0088] Effective treatments for the prevention or suppression ofsleep-related breathing disorders include systemic administration of a5-hydroxytryptamine₂ or 5-hydroxytryptamine₃ receptor antagonist eitheralone or in combination. In a preferred embodiment the serotoninreceptor antagonist has activity only in the peripheral nervous systemand/or does not cross the blood-brain barrier. In a more preferredembodiment the serotonin receptor antagonist displays both5-hydroxytryptamine and 5-hydroxytryptamine₃ receptor subtypeantagonism.

[0089] Current pharmacological treatments for sleep-related breathingdisorders also involve apnea suppression via serotonin agonist effectswithin the central nervous system, and more specifically the brainstem.Indeed, it was in view of their potential to stimulate respiration andupper airway motor outputs that serotonin enhancing drugs wereoriginally tested as pharmacological treatments for sleep apneasyndrome. One early report suggested that L-tryptophan, a serotoninprecursor, may have a beneficial effect on sleep apnea syndrome[Schmidt, Bull. Eur. Physiol. Respir., 19:625-629 (1982)]. More recentlyfluoxetine [Hanzel et al., Chest., 100:416-421 (1991)] and paroxetine[Kraiczi et al., Sleep, 22:61-67 (1999)], both selective serotoninreuptake inhibitors (SSRIs), were demonstrated to benefit some but notall patients with sleep apnea syndrome. In addition, combinations ofserotonin precursors and reuptake inhibitors reduced sleep disorderedrespiration in English bulldog model of sleep apnea syndrome [Veasey etal., Sleep Res., AS29; 1997 and Veasey et al., Am. J. Resp. Crit. CareMed., 157:A655 (1997)]. However, despite ongoing investigations theseencouraging early results with serotonin enhancing drugs have not beenreproduced.

[0090] The foregoing efforts with serotonin-enhancing drugs indicatethat the potential utility of serotonin precursors or SSRIs in apneatreatment resides strictly in their central nervous system effects.Therefore, it is precisely because the serotonin enhancing effects ofSSRIs in the peripheral nervous have been left unchecked that thesecompounds have not demonstrated reproducible effects in apnea treatment.In fact buspirone, a specific 5-hydroxytryptamine_(1A) agonist, whichstimulates respiration [Mendelson et al., Am. Rev. Respir. Dis.,141:1527-1530 (1990)], has been shown to reduce apnea index in 4 of 5patients with sleep apnea syndrome [Mendelson et al., J. Clin.Psychopharmacol., 11:71-72 (1991)] and to eliminate post-surgicalapneustic breathing in one child [Wilken et al., J. Pediatr., 130:89-94(1997). Although buspirone acts systemically, 5-hydroxytryptamine₁receptors in the peripheral nervous system have not been shown to play arole in apnea genesis. The modest apnea suppression induced by buspironeis a central nervous system effect that goes unopposed by serotonergiceffects in the peripheral nervous system.

[0091] The rationale for using SSRIs such as fluoxetine or paroxetine totreat sleep apnea syndrome rests in part on their ability to stimulateupper airway motor outputs. Applications of serotonin to the floor ofthe fourth ventricle [Rose et al., Resp. Physiol., 101:59-69 (1995)] orinto the hypoglossal motor nucleus [Kubin et al., Neurosci. Lett.,139:243-248 (1992)] produce upper airway motor activation in cats;effects which appear to be mediated predominantly by5-hydroxytryptamine₂ receptors. Conversely, systemic administration of5-hydroxytryptamine₂ receptor antagonists to English bulldogs reduceselectrical activation of upper airway muscles, diminishes upper airwaycross-sectional area and promotes obstructive apnea [Veasey et al., Am.J. Crit. Care Med., 153:776-786 (1996)]. These observations provide alikely explanation for the improvements in sleep-disordered breathingobserved in some patients following SSRI treatment.

[0092] In conjunction with the data presented herein (Examples 2 and 3)and the foregoing observations, sleep related breathing disorders (sleepapnea syndrome, apnea of infancy, Cheyne-Stokes respiration,sleep-related hypoventilation syndromes) may be effectively prevented orsuppressed via systemic administration of

[0093] (a) an agent or combinations of agents exhibiting eitherserotonin type 2 or type 3 receptor antagonism (either alone or incombination with one another) and/or in combination with either a5-hydroxytryptamine₁ or 5-hydroxytryptamine₂ receptor agonist;

[0094] (b) an agent or combination of agents or agents that exhibit bothserotonin type 2 and type 3 receptor antagonism in combination witheither a 5-hydroxytryptamine, or 5-hydroxytryptamine₂ receptor agonist;or

[0095] (c) agents that exhibit both the proper antagonistic andagonistic pharmacological profile (i.e., an agent that is both anagonist and antagonist at the receptor subtypes set forth above).

[0096] Preferred embodiments include the following:

[0097] (a) an agent or combination of agents wherein the serotoninagonist exhibits only central serotonergic actions;

[0098] (b) an agent or combination of agents wherein the serotoninagonist exhibits only central 5-hydroxytryptamine₂ actions;

[0099] (c) an agent or combination of agents s wherein the serotoninantagonist exhibits only peripheral actions while the serotonin agonistexhibits only central serotonergic actions;

[0100] (d) an agent or combination of agents that have the ability toinduce central nervous system serotonin release and that possess theantagonistic profile discussed above (i.e. both a 5-hydroxytryptamine₂and 5-hydroxytryptamine₃ receptor antagonist); or

[0101] (e) an agent or combination of agents that have the ability toinduce central nervous system serotonin release and possess onlyperipheral antagonistic effects;

[0102] Those of skill in the art will recognize that many serotoninreceptor agonists such as, but not limited to 8-OH-DPAT(8-hydroxy-2-(di-n-propylamino)tetralin, sumatriptan, L694247(2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl]-1H-indol-3yl]ethanamine),buspirone, alnitidan, zalospirone, ipsapirone, gepirone. zolmitriptan,risatriptan, 311C90, α-Me-5-HT, BW723C86(1-[5(2-thienylmethoxy)-1H-3-indolyl[propan-2-amine hydrochloride), MCPP(m-chlorophenylpiperazine), as well as others may be used in conjunctionwith serotonin receptor antagonists to prevent or amelioratesleep-related breathing disorders.

[0103] Pharmacological mechanisms of action other than serotoninprecursors or SSRIs may also be exploited to enhance central nervoussystem serotonin activity. Indeed, at least one mechanism allowsaugmented serotonin release to be selectively targeted at the centralnervous system. Specifically, antagonism of presynaptic α₂ adrenergicreceptors located on brainstem serotonergic neurons (heteroreceptors)enhances serotonin release. Selective 5-hydroxytryptamine₂ and5-hydroxytryptamine₃ receptor antagonists have been shown to blockpresynaptic α₂ -adrenoreceptors as well as postsynaptic5-hydroxytryptamine₂ and 5-hydroxytryptamine₃ receptors [deBoer, J.Clin. Psychiatr., 57(4):19-25 (19960; Devane, J. Clin. Psychiatry.,59(20):85-93 (1998); and Puzantian, Am. J. Heatlh-Syst. Pharm., 55:44-49(1998)]. Because the affinity of such agents for central α₂ receptors is10 times higher than for peripheral α₂ receptors [Puzantian, Am. J.Health-Syst. Pharm., 55:44-49 (1998)], central serotonin release isincreased with minimal adrenergic side effects such as hypertension.Thus because these pharmacological agents are high affinity antagonistsat 5-hydroxytryptamine_(2A), 5-hydroxytryptamine_(2C) and5-hydroxytryptamine₃ receptors, the net effect is increasedpost-synaptic 5-hydroxytryptamine₁ activity within the brain and reduced5-hydroxytryptamine₂ and 5-hydroxytryptamine₃ post-synaptic activity inthe central and peripheral nervous systems. Each of thesepharmacological effects serve to stimulate respiration and suppressapnea.

[0104] In view of the foregoing observations, sleep related breathingdisorders (sleep apnea syndrome, apnea of infancy, Cheyne-Stokesrespiration, sleep-related hypoventilation syndromes) may also beeffectively suppressed or prevented via systemic administration ofpharmacological agents of combinations of agents having α₂ adrenergicantagonist activity with either serotonin type 2 or type 3 receptorantagonist activity (either alone or in combination with one another).Preferred embodiments include:

[0105] (a) an agent or combination of agents wherein the α₂ adrenergicantagonist effects are exerted centrally;

[0106] (b) an agent or combination of agents wherein the serotoninantagonist effects are exerted peripherally;

[0107] (c) an agent or combination of agents wherein the α₂ adrenergicantagonist effects are exerted centrally and the serotonin antagonisteffects are exerted peripherally;

[0108] (d) the agent or combination of agents of embodiments a-c whereinthe α₂ adrenergic antagonist effect is exerted presynaptically;

[0109] (e) the agent or combination of agents of embodiments a-d whereinthe a₂ adrenergic antagonist effects are exerted selectively atpresynaptic heteroreceptors on serotonergic neurons; or

[0110] (f) the agent or combination of agents of embodiments a-d inwhich the α₂ adrenergic antagonist effect is exerted by an agent orcombination of agents possessing the following pharmacological profile:α₂ adrenergic antagonist activity with both serotonin type 2 or type 3receptor antagonist activity.

[0111] Those of skill in the art will recognize that many α₂ adrenergicreceptor antagonists such as, but not limited to phenoxybenzamine,phentolamine, tolazoline, terazosine, doxazosin, trimazosin, yohimbine,indoramin, ARC239, prazosin as well as others may be used in conjunctionwith serotonin receptor antagonists to prevent or amelioratesleep-related breathing disorders

[0112] An individual diagnosed with a sleep related breathing disorderis administered either a composition or agent having any of theforegoing pharmacological profiles in an amount effective to prevent orsuppress such disorders. The specific dose may be calculated accordingto such factors as body weight or body surface. Further refinement ofthe calculations necessary to determine the appropriate dosage fortreatment of sleep-related breathing disorders is routinely made bythose of ordinary skill in the art without undue experimentation.Appropriate dosages may be ascertained through use of established assaysfor determining dosages. Routes of administration for the foregoingmethods may be by any systemic means including oral, intraperitoneal,subcutaneous, intravenous, intramuscular, transdermal, or by otherroutes of administration. Osmotic mini-pumps and timed-released pelletsor other depot forms of administration may also be used.

[0113] Finally, those of skill in the art will recognize that withrespect to the compounds discussed above, such compounds may contain acenter of chirality. Thus such agents may exist as different enantiomersof enantiomeric mixtures. Use of any one enantiomer alone or containedwithin an enantiomeric mixture with one or more stereoisomers iscontemplated by the present invention.

[0114] Although the present invention has been described in terms ofpreferred embodiments, it is intended that the present inventionencompass all modifications and variations that occur to those skilledin the art upon consideration of the disclosure herein, and inparticular those embodiments that are within the broadest properinterpretation of the claims and their requirements. All literaturecited herein is incorporated by reference.

What is claimed is:
 1. A method of preventing or amelioratingsleep-related breathing disorder the method comprising administering toa patient in need thereof an effective amount of a serotonin receptorantagonist.
 2. The method of claim 1 wherein the sleep-related breathingdisorder is selected from the group consisting of obstructive sleepapnea syndrome, apnea of prematurity, congenital central hypoventilationsyndrome, obesity hypoventilation syndrome, central sleep apneasyndrome, Cheyne-Stokes respiration, and snoring.
 3. The method of claim1 or claim 2 wherein the serotonin receptor antagonist is selected fromthe group consisting of ketanserin, cinanserin, LY-53,857, metergoline,LY-278,584, methiothepin, p-NPPL, NAN-190, piperazine, SB-206553,SDZ-205,557, 3-tropanyl-indole-3-carboxylate,3-tropanyl-indole-3-carboxylate methiodide, methysergide, risperidone,cyproheptadine, clozapine, mianserin, ritanserin, and granisetron. 4.The method of claim 1 or claim 2 wherein the serotonin receptorantagonist is a 5-hydroxytryptamine₂ receptor subtype antagonist.
 5. Themethod of claim 1 or claim 2 wherein the serotonin receptor antagonistis a 5-hydroxytryptamine₃ receptor subtype antagonist.
 6. The method ofclaim 1 or claim 2 wherein the serotonin receptor antagonist is both a5-hydroxytryptamine₂ receptor subtype antagonist and a5-hydroxytryptamine₃ receptor subtype antagonist.
 7. A method ofpreventing or ameliorating sleep-related breathing disorders the methodcomprising administering to a patient in need thereof an effectiveamount of an agent or combination of agents having both5-hydroxytryptamine₂ subtype receptor antagonistic activity and5-hydroxytryptamine₃ subtype receptor antagonistic activity.
 8. Themethod of claim 7 wherein the sleep-related breathing disorder is Sselected from the group consisting of obstructive sleep apnea syndrome,apnea of prematurity, congenital central hypoventilation syndrome,obesity hypoventilation syndrome, central sleep apnea syndrome,Cheyne-Stokes respiration, and snoring.
 9. The method of claim 7 orclaim 8 wherein the effects of the agent or combination of agents areexerted only in the peripheral nervous system.
 10. A method ofpreventing or ameliorating sleep-related breathing disorders the methodcomprising administering to a patient in need thereof an effectiveamount of a composition comprising a serotonin receptor antagonist and aserotonin receptor agonist.
 11. The method of claim 10 wherein thesleep-related breathing disorder is selected from the group consistingof obstructive sleep apnea syndrome, apnea of prematurity, congenitalcentral hypoventilation syndrome, obesity hypoventilation syndrome,central sleep apnea syndrome, Cheyne-Stokes respiration, and snoring.12. The method of claim 10 or claim 11 wherein the serotonin receptorantagonist is selected from the group consisting of ketanserin,cinanserin, LY-53,857, metergoline, LY-278,584, methiothepin, p-NPPL,NAN-190, piperazine, SB-206553, SDZ-205,557,3-tropanyl-indole-3-carboxylate, 3-tropanyl-indole-3-carboxylatemethiodide, methysergide, risperidone, cyproheptadine, clozapine,mianserin, ritanserin, and granisetron.
 13. The method of claim 10 orclaim 11 wherein the serotonin receptor agonist is selected from thegroup consisting of 8-OH-DPAT, sumatriptan, L694247, buspirone,alnitidan, zalospirone, ipsapirone, gepirone, zolmitriptan, risatriptan,311C90, α-Me-5-HT, BW723C86, and MCPP.
 14. The method of claim 10 orclaim 11 wherein the serotonin receptor antagonist is a5-hydroxytryptamine₂ receptor subtype antagonist.
 15. The method ofclaim 10 or claim 11 wherein the serotonin receptor antagonist is a5-hydroxytryptamine₃ receptor subtype antagonist.
 16. The method ofclaim 10 or claim 11 wherein the serotonin receptor agonist is a5-hydroxytryptamine₁ receptor subtype agonist.
 17. The method of claim10 or claim 11 wherein the serotonin receptor agonist is aS-hydroxytryptamine₂ receptor subtype agonist.
 18. The method of claim10 or claim 11 wherein the effects of the serotonin receptor agonist areexerted in the central nervous system.
 19. The method of claim 10 orclaim 11 wherein the effects of the serotonin receptor antagonist areexerted in the peripheral nervous system.
 20. The method of claim 10 orclaim 11 wherein the effects of the serotonin receptor agonist areexerted in the central nervous system and wherein the effects of theserotonin receptor antagonist are exerted in the peripheral nervoussystem.
 21. The method of claim 10 or claim 11 wherein the serotoninreceptor antagonist exhibits both 5-hydroxytryptamine₂ and5-hydroxytryptamine₃ receptor subtype antagonistic activity.
 22. Amethod of preventing or ameliorating sleep-related breathing disordersthe method comprising administering to a patient in need thereof aneffective amount of an agent or combination of agents exhibiting both5-hydroxytryptamine₂ and 5-hydroxytryptamine₃ receptor subtypeantagonistic activity and wherein the agent or combination of agentsfurther exhibits the ability to induce serotonin release within thecentral nervous system.
 23. The method of claim 22 wherein thesleep-related breathing disorder is selected from the group consistingof obstructive sleep apnea syndrome, apnea of prematurity, congenitalcentral hypoventilation syndrome, obesity hypoventilation syndrome,central sleep apnea syndrome, Cheyne-Stokes respiration, and snoring.24. The method of claim 21 or claim 22 wherein the agent or combinationof agents demonstrate the serotonin receptor antagonistic activity onlyin the peripheral nervous system.
 25. A method of preventing orameliorating sleep-related breathing disorders the method comprisingadministering to a patient in need thereof an effective amount of anagent or composition exhibiting a2 adrenergic receptor subtypeantagonism and either 5-hydroxytryptamine₂ or 5-hydroxytryptamine₃receptor subtype antagonism or both.
 26. The method of claim 25 whereinthe sleep-related breathing disorder is selected from the groupconsisting of obstructive sleep apnea syndrome, apnea of prematurity,congenital central hypoventilation syndrome, obesity hypoventilationsyndrome, central sleep apnea syndrome, Cheyne-Stokes respiration, andsnoring.
 27. The method of claim 25 or claim 26 wherein the serotoninreceptor antagonist is selected from the group consisting of ketanserin,cinanserin, LY-53,857, metergoline, LY-278,584, methiothepin, p-NPPL,NAN-190, piperazine, SB-206553, SDZ-205 ,557,3-tropanyl-indole-3-carboxylate, 3-tropanyl-indole-3-carboxylatemethiodide, methysergide, risperidone, cyproheptadine, clozapine,mianserin, ritanserin, and granisetron.
 28. The method of claim 25 orclaim 26 wherein the α₂ adrenergic receptor subtype antagonist isselected from the group consisting of phenoxybenzamine, phentolamine,tolazoline, terazosine, doxazosin, trimazosin, yohimbine, indoramin,ARC239, and prazosin.
 29. The method of claim 25 or claim 26 wherein theα₂ adrenergic antagonist effects are exerted within the central nervoussystem.
 30. The method of claim 25 or claim 26 wherein the serotoninantagonist effects are exerted in the peripheral nervous system.
 31. Themethod of claim 25 or claim 26 wherein the α₂ adrenergic antagonisteffects are exerted in the central nervous system and the serotoninantagonist effects are exerted in the peripheral nervous system.
 32. Themethod of claim 29 wherein the α₂ adrenergic antagonist effect isexerted presynaptically.
 33. The method of claim 30 wherein the α₂adrenergic antagonist effect is exerted presynaptically.
 34. The methodof claim 31 wherein the α₂ adrenergic antagonist effect is exertedpresynaptically.
 35. The method of claim 29 wherein the wherein the α₂adrenergic antagonist effects are exerted selectively at presynapticheteroreceptors located on serotonergic neurons.
 36. The method of claim30 wherein the wherein the α₂ adrenergic antagonist effects are exertedselectively at presynaptic heteroreceptors located on serotonergicneurons.
 37. The method of claim 31 wherein the wherein the α₂adrenergic antagonist effects are exerted selectively at presynapticheteroreceptors located on serotonergic neurons.